A novel and efficient one-pot synthesis of furo[3′,4′:5,6]pyrido[2,3-c]pyrazole derivatives using organocatalysts

Synthetic strategies of heterocycle-integrated pyridopyrimidine scaffolds supported by nano-catalysts

Nano-catalysts are of special character for the synthesis of organic molecules with high efficiency, and exceptional physicochemical properties. The objective of this study was to present an overview of the literature reports concerning the synthetic strategies supported by nano-catalysts and the biological features of heterocycle-integrated pyridopyrimidine scaffolds. The basic topics include the strategies that were adopted to prepare pyrido[2,3-d]pyrimidines and pyrido[1,2-a]pyrimidines. The synthesis of pyrido[2,3-d]pyrimidines was attained through two-, three-, or four-component reactions. The synthesis of spirocyclic systems, including spiro[indoline-pyridopyrimidine] derivatives and arylation reactions, was investigated. The anticipated mechanisms of the diverse target products, in addition to the preparation of the nanocatalysts, were scrutinized. The privileged antimicrobial characteristics, challenges, literature overview, and future prospectives were consistently investigated.

1H-Pyrazolo[3,4-b]pyridines: Synthesis and Biomedical Applications

Pyrazolo[3,4-b]pyridines are a group of heterocyclic compounds presenting two possible tautomeric forms: the 1H- and 2H-isomers. More than 300,000 1H-pyrazolo[3,4-b]pyridines have been described which are included in more than 5500 references (2400 patents) up to date. This review will cover the analysis of the diversity of the substituents present at positions N1, C3, C4, C5, and C6, the synthetic methods used for their synthesis, starting from both a preformed pyrazole or pyridine, and the biomedical applications of such compounds.

Organocatalysts based on natural and modified amino acids for asymmetric reactions

Small organic molecules predominantly containing C, H, O, N, S and P element are found promising molecule to accelerate chemical reactions and are named organocatalysis. In addition, these organocatalysts are easy availability, stable in water and air, inexpensive, and low toxicity, which confer a huge direct application in organic synthesis when compared to transition metal catalyzed reactions and becoming powerful tools in the construction of a selective chiral product. Interest on organocatalysis is spectacularly increased since last two decades, due to the novelty of the concept and selectivity. Based on the nature of the organocatalysts used, they are classified in to four major classes, among them one of the types is amino acids derived organocatalysts. Natural amino acids are playing important role in building blocks of protein construction, and also intermediate products of the metabolism. α-Amino acid is a molecule, that contains both amine and carboxyl functional group. Their particular structural characteristic determines their role in protein synthesis, and bifunctional asymmetric catalysts for stereoselective synthesis. Two functional groups present on a single carbon acting as an acid and base, which promote chemical transformations in concert similar to the enzymatic catalysis. The post translational derivatives of natural α-amino acids include 4-hydroxy-L-proline and 4-amino-L-proline scaffolds, and its synthetic variants based organocatalysts, whose catalytic activity is well documented. This chapter discussed past and present development of the organocatalysts derived from natural and modified amino acids for various important organic transformations reviewed.

New frontiers in the transition-metal-free synthesis of heterocycles from alkynoates: an overview and current status

This review highlights the successful utilization of transition-metal-free approaches for the modular assembly of various heterocycles from alkynoates.

Synthesis of Pyrazolo-Fused 4-Azafluorenones in an Ionic Liquid. Mechanistic Insights by Joint Studies Using DFT Analysis and Mass Spectrometry

A series of pyrazolo-fused 4-azafluorenones (indeno[1,2-b]pyrazolo[4,3-e]pyridines, IPP) were synthesized via the three-component reaction between arylaldehydes, 3-methyl-1H-pyrazol-5-amine and 1,3-indanedione in an ionic liquid as a catalyst at room temperature. The applied synthetic route has the advantages of easy work-up under mild reaction conditions presenting moderate yields and an environmentally benign procedure. A theoretical study based on conceptual-density functional theory has been done, bond reactivity indices have been calculated and an electrophilic and nucleophilic character of localized orbitals has been determined to analyze the possible electronic mechanisms.

One pot multi-component synthesis of functionalized spiropyridine and pyrido[2,3-d]pyrimidine scaffolds and their potent in-vitro anti-inflammatory and anti-oxidant investigations

A new series of functionalized fused pyridines 4(a-i) and fused pyrido[2,3-d]pyrimidines 8(a-c) were designed and synthesized through a multi-component reaction where in pyridine ring formation step plays a key role. All the newly formed compounds were well characterized by spectral techniques such as FTIR, ¹ HNMR, ¹³ CNMR, HRMS and XRD. The potential therapeutic activities such as anti-inflammatory activity by protein denaturation and RBC membrane stabilization methods, and anti-oxidant activity by DPPH scavenging method of the newly synthesized compounds were studied. Interestingly, in-vitro testing of these compounds reveals that the compounds 4d, 4g, 4i, 8a and 8b showed comparable anti-inflammatory activity with respect to the standard drug, diclofenac. Similarly, fused pyridine 4f showed excellent anti-oxidant activity when compared with the standard, ascorbic acid.

Microwave-assisted one-pot synthesis in water of carbonylpyrazolo[3,4-b]pyridine derivatives catalyzed by InCl3 and sonochemical assisted condensation with aldehydes to obtain new chalcone derivatives containing the pyrazolopyridinic moiety

Pyrazolo[3,4-b]pyridines derivatives have been synthesized via one-pot condensation of 3-methyl-1-phenyl-1H-pyrazolo-5-amine (1), paraformaldehyde (2) and β-diketones (3) under microwave irradiation in aqueous media catalyzed by InCl₃.

Efficient synthesis of functionalized benzo[b][1,8]naphthyridine derivatives via three-component reaction catalyzed by L-proline

A facile and efficient one-pot procedure for the preparation of functionalized benzo[b][1,8]naphthyridine derivatives by three-component reaction of 2-chloroquinoline-3-carbaldehyde, 1,3-dicarbonyl compounds, and enaminones catalyzed by l-proline is described. This new protocol has the advantages of environmental friendliness, good yields, and convenient operation.

Regioselective Synthesis and Antibacterial Evaluation of a New Class of Substituted Pyrazolo[3,4-b]Pyridines

New derivatives of polyfunctional pyrazolo[3,4- b]pyridines were synthesised via a regioselective one-pot three-component reaction of 3- (cyanoacetyl)indole, 5-amino-3-methylpyrazole and arylaldehydes in excellent yields using Fe3+-montmorillonite as a reusable catalyst under conventional conditions and ultrasonic irradiation. In particular, valuable features of this method include high reaction rate, employment of a reusable catalyst, straightforward procedure, the easy work-up of the products and mild reaction conditions. The antibacterial activities of the synthesised products were examined which showed promising activities.

l-Proline-catalysed three-component Cascade Reaction for the Facile Synthesis of 3,4-dihydro-2H-pyrano[3,2-c]quinolin-2,5(6H)-dione Derivatives

A series of 4-aryl-3,4-dihydro-2 H-pyrano[3,2- c]quinolin-2,5(6 H)-dione derivatives was synthesised by the three-component reaction of aromatic aldehyde, quinoline-2,4-diol and Meldrum's acid catalysed by l-proline. This protocol has the advantages of easy work-up, mild reaction conditions and high yields.

An efficient one-pot synthesis of pyrano[3,2-c]quinolin-2,5-dione derivatives catalyzed by L-proline

A series of 4-aryl-6-methyl-3,4-dihydro-2H-pyrano[3,2-c]quinolin-2,5(6H)-diones were synthesized via the three-component reactions of aromatic aldehydes, 4-hydroxy-1-methylquinolin-2(1H)-one, and Meldrum's acid catalyzed by L-proline. The structures of the products were identified by spectroscopic analysis. A mechanism for this three-component reaction catalyzed by L-proline was proposed.

One-pot, three-component synthesis of 7-azaindole derivatives from N-substituted 2-amino-4-cyanopyrroles, various aldehydes, and active methylene compounds

An efficient and practical route to 7-azaindole framework has been developed by one-pot, three-component cyclocondensation of N-substituted 2-amino-4-cyanopyrroles, various aldehydes, and active methylene compounds in ethanol or acetic acid at reflux. Reactions involving tetronic acid, indane-1,3-dione, dimedone, and 5-phenylcyclohexane-1,3-dione gave carbocyclic fused 7-azaindoles, whereas Meldrum's acid, benzoylacetonitrile, and malononitrile resulted in the highly substituted 7-azaindole derivatives, making this strategy very useful in diversity-oriented synthesis (DOS).

Green Synthesis of Chromen-2-One Derivatives Catalysed by L-Proline

A series of chromen-2-one derivatives was synthesised by the reaction of 4-hydroxy-6-methyl-2H-pyran-2-one with substituted 2-hydroxybenzaldehydes catalysed by L-proline. This protocol has the advantages of easy workup mild reaction conditions and high yields.